This is an open-label, three center, randomized, multiple-dose, two-group, parallel treatment study. An attempt will be made to match the patients in the two groups by age. One treatment group will consist of 24 non-pregnant female patients diagnosed with bacterial vainosis and the other treatment group will consist of 24 patients in their second to third trimester of pregnancy requiring treatment for bacterial vaginosis. The primary objective of this study is to compare the steady-state pharmacokinetics of metronidazole, after a daily oral dose of Flagyl ER (metronidazole extended release tablets, 750 mg), administered for 7 days between non-pregnant female patients and patients in their second to third trimester of pregnancy requiring treatment for bacterial vaginosis. The secondary objective of this study is to compare the safety and effectiveness of Flagyl ER in non-pregnant and pregnant patients requiring treatment for bacterial vaginsosi.